a) Field of the Invention
This invention relates to a stepping motor. More specifically, this invention relates to a method of insulation between a coil and a stator core.
b) Description of the Related Art
Generally, a stepping motor comprises a rotor part having a magnet fixed onto a stepping a stepping motor comprises a rotor part having a magnet fixed onto a rotor shaft, a stator part facing the rotor part, a circular coil bobbin, and a coil wound around the body of the coil bobbin.
In order to attain miniaturization of such a stepping motor, in the case of a motor size of less than 10 mm in diameter for example, the bobbin size has been reduced by integrating the coil bobbin into the inner stator core constituting the stator part by means of insert molding.
Furthermore, when the motor size is less than 5 mm in diameter in which a coil bobbin is molded with the inner stator core as an integrated body, the coil bobbin occupies a large proportion of the motor. As a result, the required winding space cannot be secured and the needed motor torque cannot be obtained.
To overcome this problem, an insulating film is formed on the surface of the stator core, and the coil bobbin is omitted to eliminate the proportion occupied by the coil bobbin. A stepping motor having an elongated space for coil winding has been thus developed (see Unexamined Japanese Patent Application Publication No. 2004-112985, for example). In order for a stepping motor of this type to acquire good motor characteristics, it is essential to have a magnetic coupling with little magnetic reluctance between an inner stator core and an outer stator core. Therefore, in the stepping motor shown in said Unexamined Japanese Patent Application Publication No. 2004-112985, when insulating films are formed on an inner stator core and an outer stator core, in order to secure a good magnetic coupling, a masking process is provided so that an insulation film is not formed on the junction between the inner stator core and the outer stator core.